There are three main parameters in the advanced settings menu: Gas Limit, Nonce and input data. This article will explain what these are and how to use them properly.
The Gas Limit is the maximum amount of gas that the transaction will use. If the advanced settings menu is untouched, it will automatically be set to 21000 for basic ethereum transfers. For token transfers, Coinomi will automatically calculate a gas limit, which is usually higher than 21000. A higher gas limit is usually necessary for sending tokens or other contracts (myetherwallet recommends ~200,000 for tokens). In Coinomi, gas limit is calculated to be the same as the gas used. Therefore, you do not need to worry about gas limits when participating in ICOs or when sending ETH or tokens to contract addresses. The work will be done behind the scenes and the correct limit will be set. If the gas limit is too high, only the amount actually used will count towards your transaction fee, after the transaction is confirmed.
The Nonce is a value that increases after every sent transaction. Your transaction will not be mined unless
- All previous nonce values have been confirmed and
- The nonce in your transaction is the highest nonce to date.
The nonce value should not be changed in advanced settings unless you are trying to replace an unconfirmed transaction. Read more here.
The Input Data field is for entering specific data required in some transactions. For most users this will never be used manually as transactions which require such data automatically fill this, For example Dapp/DEX transactions.
Aside from the 'advanced settings' menu, when sending you are given 4 options for setting your transaction fees/gas price. Three dynamic settings, LOW/NORMAL/HIGH, are calculated with the current conditions of the ETH network in mind to help you select a fee which is sufficient for sending at a given moment. You are also offered a 'custom' option which has a default set value of 20gwei -- Setting the 'custom' option too low can cause your transaction to become stuck waiting for confirmation for days or even weeks.
The Gas Price is the price (in ETH) that you are paying for each unit of Gas. If you do not adjust any values in the advanced settings menu, then your ethereum transaction will process with the Gas Price set in "Settings - Advanced settings - transaction fees - Ethereum" (default is 20 Gwei or 0.00000002 ETH). For example, if you have the default Gas Price of 0.00000002 ETH, and your Gas Limit is 21000, then for the transaction, you will pay at most (21000 gas)*(0.00000002 ETH/gas) = 0.00042 ETH. Once it is confirmed, any amount paid for gas that wasn't used will be returned. To estimate proper gas prices based on market conditions, you can use this tool: https://ethgasstation.info/calculatorTxV.php
Note 1: Please do not change these parameters unless you know what you are doing. Doing so could result in irreversible, extremely high fees, an unconfirmed transaction, a failed transaction with loss of transaction fees.
Note 2: Higher gas prices can be advantageous if there are many ethereum transactions in the mempool and you need yours to be mined quickly. For example, at the beginning of a capped ICO, you may need to contribute your ether more quickly than other people. Manually raising the price of gas will increase the chances that your transaction is included in a block.